* Hannes Dorbath:
> + Hardware Raids might be a bit easier to manage, if you never spend a
> few hours to learn Software Raid Tools.
I disagree. RAID management is complicated, and once there is a disk
failure, all kinds of oddities can occur which can make it quite a
challenge to get back a non-degraded array.
With some RAID controllers, monitoring is diffcult because they do not
use the system's logging mechanism for reporting. In some cases, it
is not possible to monitor the health status of individual disks.
> + Using SATA drives is always a bit of risk, as some drives are lying
> about whether they are caching or not.
You can usually switch off caching.
> + Using hardware controllers, the array becomes locked to a particular
> vendor. You can't switch controller vendors as the array meta
> information is stored proprietary. In case the Raid is broken to a
> level the controller can't recover automatically this might complicate
> manual recovery by specialists.
It's even more difficult these days. 3ware controllers enable drive
passwords, so you can't access the drive from other controllers at all
(even if you could interpret the on-disk data).
> + Even battery backed controllers can't guarantee that data written to
> the drives is consistent after a power outage, neither that the drive
> does not corrupt something during the involuntary shutdown / power
> irregularities. (This is theoretical as any server will be UPS backed)
UPS failures are not unheard of. 8-/ Apart from that, you can address
a large class of shutdown failures if you replay a log stored in the
BBU on the next reboot (partial sector writes come to my mind).
It is very difficult to check if the controller does this correctly,
though.
A few other things to note: You can't achieve significant port density
with non-RAID controllers, at least with SATA. You need to buy a RAID
controller anyway. You can't quite achieve what a BBU does (even if
you've got a small, fast persistent storage device) because there's
no host software support for such a configuration.
